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85 R80 stalls when throttle applied from idle

The engine of my 85 R80 intermittently stalls when I open the throttle to accelerate from a stop. I was able to duplicate the concern while standing beside the bike and noted a popping sound and saw a puff of smoke from the right carb.

It concerns me when it happens at a intersection when the light turns green.

I'm posting this because I'd like to understand what's happening when it stalls and why. Thanks for your input.

Sounds like maybe your idle circuit needs tweaking or you need a carb synch. Try changing the idle air mixture screw small turns (1/8 to 1/4) in one direction on both carbs. See if the problem improves or gets worse. If you find one direction helps, then consider checking the entire carb synch process to get it dialed in better.

JIm, when was the last time you went through the ignition adjustment / plugs/ valves drill? It's always nice to know when everything is "zeroed" out.

The last time I encountered a "popping and spitting" situation it turned out to be tiny bit of grit that found it's way to the right side main jet. When was the last time your carburetors were off and cleaned?

"It is what you discover, after you know it all, that counts." _ John Wooden

Thanks Lew. The last time the carbs were done was 2008. I plan on taking the bike to the local airhead tech for this and to have the splines lubed for another problem I'm having. In the mean time I'm trying to gain an understanding of what's going on. Jim.

I would check the diaphragm in the right carburetor. The diaphragm is moved up-and-down by the pressure difference caused by the different speed of the air through the carburetor tunnel. At low throttle opening there is less air per second going through which causes a minimal pressure difference between both sides of the diaphragm and hence the jet needle attached to the diaphragm hangs low and thus only a small amount of fuel evaporates into the airstream. Under full throttle opening the large amount of airflow causes a vaccum in the dome above the diaphragm and hence the jet needle is raised and more fuel is entering the tunnel.

This techique gives a pretty good air-to-fuel ratio at all throttle positions given no modern schnick-schnack (fuel injection, senors-sensors-sensors, electronic control).

If the diaphragm is torn a sudden opening of the throttle would not cause the diaphragm to lift and you have a far too lean air/fuel mixture. Depending on the damage of the diaphragm it may eventually regain position in relation to the throttle position and airflow per second.

A story: When I rebuild my R100GS' carburetors back when I didn't watch carefully when I positioned the diaphragm under the dome in the carburetor. There's a notch that is used to align both. In my case it was off (turned) by a couple of degrees. The motor reacted erractically at low throttle positions but worked pretty normal at above 2,000 RPMs.

In the past, I've heard people report that their bike seemed to run fine at lower speeds but couldn't go above a certain speed. Typically, that's due to a torn diaphragm where at the higher speeds and higher vacuums, the tear doesn't allow the equalization. Plus at higher speeds, the idle circuit is less effective. But at lower speeds, while the raising and lower of the slide is important, the idle circuit is still contributing which could be the reason a bike might run OK at lower speeds with a torn diaphragm. So, I would think that if the bike runs well at freeway speeds, it's probably not the diaphragm. We never heard about that from the PO.